The invention relates to the field of wood burning furnaces and comprises a high efficiency furnace having an aperture for the removal of accumulated creosote from the heat exchanger.
With the rising cost of operating electric and gas fired furnaces has come an increased interest in wood burning furnaces and an effort to utilize firewood when such wood is inexpensive and available. Rising demand for wood burning furnaces has encouraged efforts to make the wood furnace more energy efficient and also more adaptable to existing buildings having already installed gas fired or electric heating systems. In addition, there are a growing number of mobile homes and trailers, particularly in outlying areas, which would utilize wood burning furnaces if the furnaces could be safely and effectively combined with the existing gas fire furnaces typically used with such trailers and mobile homes. In situations where the wood furnace is to be used in combination with an existing home heating system, it is helpful to be able to position the wood furnace outside the home or trailer. Such external positioning eliminates indoor smoke odors as well as eliminating the need to move sometimes dirty firewood into the home and to carry the ashes outdoors. In some geographic areas, building code restrictions can also be less demanding for an externally positioned wood furnace.
In order to reduce the amount of wood consumed by such a furnace and to prolong the burning time with a given quantity of wood, more efficient furnaces with improved heat exchangers are desirable. Typically such efficiency is gained by constructing the heat exchanger to extract more heat from the hot air and smoke passing through the exchanger before exhausting the air and smoke from the furnace chimney. Efficiency can be noticably increased by having the heat exchanger be a tightly closed doorless chamber with minimal external openings through which heat loss can occur. It has been found, however, that as the heat exchanger successfully removes more and more heat from the smoke within it, that the amount of creosote deposited from the smoke onto the heat exchanger increases. Such deposits of creosote can be undesirable because they tend to insulate the heat exchanger walls from the smoke and thereby progressively reduce later heat transfer, and additionally, such creosote can eventually create a fire hazard, producing secondary fires in the exchanger and chimney. Accordingly, it is desirable to not only increase the efficiency of the heat exchanger but to also provide a means to intermittently purge the interior of the closed heat exchanger of such creosote deposits and to dispose of the creosote. The present invention provides an improved heat exchanger of high efficiency and a means for effectively removing the creosote from the heat exchanger.